A known machine compresses or conveys fluid by making use of changes in the volume of a compression chamber formed by a flexible membrane and the inner wall of a casing, the changes being brought about by reciprocation of the membrane. This membrane consists of a diaphragm or bellows mounted in the casing. A diaphragm type pump in which a diaphragm is used as the flexible membrane is disclosed in Japanese Patent Laid-Open No. 246569/1988.
Stress produced in a diaphragm or bellows is caused either by displacement or by pressure. The difference between the pressures inside and outside the compression chamber increases as the applied pressure increases. Since the diaphragm is subjected to great pressure differences, the diaphragm bends greatly, and the stress increases. This deteriorates the durability of the diaphragm. Also, the capability to compress fluid is impaired by the flexure. Furthermore, the rate of flow decreases. For these reasons, it has been heretofore impossible to use diaphragm type or bellows type compressors in high-pressure applications.